iron and individual sections shall be replaceable. A manual adjustment
shall be provided to regulate the ash bed thickness and ashes shall be
automatically discharged to the ash pit. The front of the grates where the
ash is discharged shall be enclosed with a dust-tight enclosure of heavy
cast-iron plates not less than 15.9 mm 5/8 inch thick and properly
protected with firebrick where exposed to the furnace, or shall be of
refractory-lined steel plate. The vertical fronts of this enclosure shall
be fitted with refractory-lined inspection and access doors, one to each
feeder. Roof of this enclosure shall be sealed with refractory for
protecting the metal parts from the furnace temperature. The underside of
the grates shall be enclosed to form a chamber with a hopper for receiving
the ashes. Over-fire air jets shall be provided for turbulence and
2.3.1.4
Stoker Controls
Stoker controls that accurately regulate the coal feed rate shall be of the
type required for connection to the combustion control system. Manual
setting of the coal feed rate with variation of stoker feed, as required to
maintain any desired capacity between 50 and 110 percent of boiler
capacity, shall be possible without disconnecting linkage. Separate feeder
and grate drives shall be provided. Grate shall be driven through a
variable speed transmission with devices for changing speed interlocked
with fuel feed regulation. Manual adjustment of grate speed shall only be
for allowing synchronization with fuel feed. All gears and chains of the
variable speed transmission and gear reduction units, as required, shall
run in a bath of oil and be enclosed in a dust-tight and oil-tight case.
Front and rear shafts of the grates shall be fitted with a forced
lubrication system with fittings located outside the setting. All bearings
shall be of the antifriction type with hardened inner and outer races
fitted with dust seals and easily accessible forced lubrication fittings.
Stoker [and grate] shall be provided with safety release devices to protect
the mechanism from foreign materials or obstructions. Stoker shall be
driven by [electric motor] [steam turbine]. [Electric motor shall be
totally enclosed fan-cooled for installation in Class II, Division 1, Group
F hazardous location in accordance with NFPA 70. Motor starter shall be
magnetic [across-the-line] [reduced voltage start] type with
[general-purpose] [dust-tight] [explosion-proof] enclosure.] [Steam
turbines utilized for stoker drives shall conform to NEMA SM 23.]
2.3.1.5
Hoppers
Hoppers shall be constructed of steel plates not less than 6.4 mm 1/4 inch
thick and shall have a capacity of not less than [_____] kg pounds per
feeder. Hoppers shall be provided with clean-out doors in the front of
each feeder. Coal feed to the hoppers shall be fitted with concave type
transitions to ensure the proper distribution of coal and coal fines across
the width of the hoppers. Stoker front plate shall form the front of the
boiler for the full width of the boiler and from the firing floor to some
point above the stoker where it shall connect to the boiler structural
framing. Front shall be cast-iron or steel plate refractory lined with
[auxiliary firing doors and] clean-out doors of refractory lined cast-iron.
Structural framing as required shall support the stoker and its components
from the boiler foundation or boiler room floor. The area under the grates
shall be divided into not less than four airtight zones for supply of
forced draft having zone control dampers with external indicating operating
and locking devices. All pressure parts for water-cooled grates including
watertubes, headers, and valves furnished by the stoker manufacturer shall
be for boiler pressure specified and shall be constructed in conformance
SECTION 15559A
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